Gradient induced particle motion in suspensions

ABSTRACT

Methods of inducing or controlling particle motion in suspensions and colloids are described. In one aspect, a method of inducing particle motion in a suspension comprises contacting the suspension with a gas phase to establish at least one interface between the gas phase and continuous phase of the suspension. One or more gases of the gas phase are transferred across the interface to provide a solute gradient in the continuous phase, the solute gradient inducing motion of the suspended particles.

RELATED APPLICATION DATA

The present application claims priority pursuant to 35 U.S.C. § 119(e)to U.S. Provisional Patent Application Ser. No. 62/469,755, filed Mar.10, 2017 and to International Application PCT/US2017/049819, filed Sep.1, 2017, both of which are hereby incorporated by reference in theirentireties.

FIELD

The present invention relates suspensions and colloidal compositionsand, in particular, to methods of inducing or affecting particle motionin suspensions and colloids.

BACKGROUND

Particle motion or transport in suspensions and colloids is important inmany applications including drug delivery, disinfection and filtration.Several mechanisms exist to induce directed motion of colloidalparticles, such as employment of one or more external forces. Externalforces can include electrostatic, dielectric, magnetic, acoustic,optical and/or inertial effects. Effective application of externalforces can necessitate apparatus of complex architecture and design.Moreover, filtration of colloidal compositions often requiressubstantial amounts of energy and expensive apparatus comprising one ormore membranes having pore size suitable for capture of ultrafineparticles. Additionally, such filtration apparatus require routinemaintenance to preclude membrane clogging or fouling.

SUMMARY

In view of these disadvantages, new methods of inducing or controllingparticle motion in suspensions and colloids are needed. In one aspect, amethod of inducing or affecting particle motion in a suspensioncomprises contacting the suspension with a gas phase to establish atleast one interface between the gas phase and continuous phase of thesuspension. One or more gases of the gas phase are transferred acrossthe interface to provide a solute gradient in the continuous phase, thesolute gradient inducing or affecting motion of the suspended particles.In some embodiments, for example, the solute gradient induces thesuspended particles to move toward the interface of the gas phase andcontinuous phase. In other embodiments, the solute gradient induces thesuspended particles to move away from the interface.

In another aspect, analytical methods are described. In someembodiments, an analytical method comprises providing a suspension in achamber, the suspension comprising analyte particles suspended in acontinuous phase. The suspension is contacted with a gas phase toestablish at least one interface between the gas phase and continuousphase. One or more gases of the gas phase are transferred across theinterface to provide a solute gradient in the continuous phase, thesolute gradient concentrating the analyte particles in a region of thechamber. The concentrated analyte particles can subsequently be detectedand/or one or more properties of the analyte particles can bedetermined. In some embodiments, for example, analyte particles arepresent in the suspension at such low concentration that the particlescannot be readily detected. However, sufficient concentration of theanalyte particles induced by the solute gradient can render theparticles detectable.

In another aspect, methods of detecting soluble gases are described. Amethod of detecting a soluble gas comprises providing a suspension in achamber and contacting the suspension with a gas sample to establish atleast one interface between the gas sample and continuous phase of thesuspension. Particle motion is detected in response to a solute gradientproduced by dissolution of one or more gases from the sample aftercrossing the interface.

In a further aspect, methods of inhibiting fouling of surfaces incontact with fluids are described. A method of inhibiting fouling of asurface in contact with a fluid comprises contacting the fluid with agas phase to establish at least one gas-fluid interface. One or moregases of the gas phase are transferred across the interface to provide asolute gradient in the fluid, the solute gradient inducing particlemotion in the fluid away from the surface. In some embodiments, forexample, the gas-fluid interface is adjacent to the surface, and thesolute gradient repels the particles from the surface. In otherembodiments, the gas-fluid interface is spaced apart from the surface,and the solute gradient attracts particles, thereby directing particlemotion away from the surface.

These and other embodiments are described in further detail in thedetailed description which follows.

DETAILED DESCRIPTION

Embodiments described herein can be understood more readily by referenceto the following detailed description and examples and their previousand following descriptions. Elements, apparatus and methods describedherein, however, are not limited to the specific embodiments presentedin the detailed description and examples. It should be recognized thatthese embodiments are merely illustrative of the principles of thepresent invention. Numerous modifications and adaptations will bereadily apparent to those of skill in the art without departing from thespirit and scope of the invention.

I. Gradient Induced Particle Motion

In one aspect, a method of inducing or affecting particle motion in asuspension comprises contacting the suspension with a gas phase toestablish at least one interface between the gas phase and continuousphase of the suspension. One or more gases of the gas phase aretransferred across the interface to provide a solute gradient in thecontinuous phase, the solute gradient inducing or affecting motion ofthe suspended particles. In some embodiments, for example, the solutegradient induces the suspended particles to move toward the interface ofthe gas phase and continuous phase. In other embodiments, the solutegradient induces the suspended particles to move away from theinterface.

Turning now to specific components, the suspension continuous phase cancomprise any species not inconsistent with the objectives of the presentinvention. In some embodiments, the continuous phase exhibits proticcharacter. For example, the continuous phase can be water oraqueous-based. When aqueous-based, the continuous phase may compriseother protic species including carboxylic acids, alcohols, amines ormixtures thereof. Aqueous-based continuous phase may also include one ormore polar aprotic species such as N-methylpyrrolidone, acrylonitrile,acetone, tetrahydrofuran (THF), ethyl acetate, acetone,dimethylformamide (DMF), acetonitrile or dimethyl sulfoxide (DMSO) orvarious mixtures thereof. In some embodiments, the continuous phase cancomprise one or more species operable to react with gas for iongeneration. As described further herein, ions generated by reaction ofgas with the continuous phase can produce an ion concentration gradientfor inducing particle motion in the suspension. Species of thecontinuous phase interfering with or precluding the formation of an ionconcentration gradient upon introduction of a gas into or removal of agas from the continuous phase should generally be avoided, but may bepresent in low concentrations.

However, species can be added to the continuous phase to affect one ormore properties of the ion concentration gradient produced bydissolution of gas in the continuous phase. In some embodiments, anadditive to the continuous phase can enhance or retard thestrength/diffusion potential of the ion concentration gradient. In otherembodiments, an additive can increase or diminish duration of the ionconcentration gradient. Additives can comprise various ionic speciessuch as salts and/or acids. Additives can also comprise protic and polaraprotic species described above. Compositional identity and/or amount ofadditive can be selected according to several considerations, includingbut not limited to, the specific identities of the continuous phase andgas phase, particle composition and surface charge, as well as thedesired effect on the ion concentration gradient. In some embodiments,additive(s) can be added to the continuous phase to assist in selectiveseparation of suspended particles.

In addition to the foregoing polar liquids, the continuous phase maycomprise one or more hydrophobic or non-polar liquids, in someembodiments. Gases dissolved in a non-polar continuous phase may producecompositional gradients in the continuous phase operable for affectingor inducing motion of the suspended particles. Accordingly, solutegradients affecting particle motion in the suspension include gradientsof dissolved gas molecules in addition to ionic gradients formed byreaction of one or more gases with the continuous phase. Gradients ofdissolved gas molecules can also be present in polar or hydrophiliccontinuous phases.

In further embodiments, the continuous phase may be a gas as opposed toa liquid. For example, a gaseous continuous phase may comprise watervapor or a mixture of water vapor with other gases. A gaseous continuousphase, in some embodiments, is operable to react with one or more gasesto provide ion concentration gradients for affecting or inducingmovement of particles suspended in the continuous phase. In this way,particle concentration and/or separation techniques based on inducedparticle movement are not limited to liquid phase applications.

As described herein, the suspension is contacted with a gas phase toestablish at least one interface between the gas phase and continuousphase of the suspension. The gas phase comprises at least one gas thatis soluble in the continuous phase. In some embodiments, the gas phasecan comprise a plurality of gases soluble in the continuous phase. Thegas phase can contact the continuous phase in any desired manner toestablish an interface between the gas phase and continuous phase. Insome embodiments, the gas phase is flowed over a surface of thecontinuous phase. In such embodiments, a continuous or uninterruptedinterface is formed between the gas phase and continuous phase.Alternatively, a discontinuous interface can be formed between the gasphase and the continuous phase. For example, a porous membrane can bepositioned between the gas phase and continuous phase. Pores of themembrane passing one or more gases of the gas phase into or out of thecontinuous phase establish an interrupted or discontinuous interface. Infurther embodiments, the gas phase can be bubbled or injected into thecontinuous phase. Bubbling or injecting can create multiple independentinterfaces between the gas phase and continuous phase.

One or more gases of the gas phase are transferred across the interfaceto provide solute gradient(s) affecting motion of the suspendedparticles. The solute gradient can be compositional in nature whereinparticle motion is affected by amount(s) of gas dissolved in thecontinuous phase. In other embodiments, the solute gradient can be anion concentration gradient formed by reaction of the gas with thecontinuous phase to provide ionic species. The ionic species can exhibitlarge differences in their diffusivities in the continuous phase,thereby providing a large diffusion potential. Solubility of one or moregases in the continuous phase will necessarily depend on compositionalidentity of the continuous phase. In some embodiments wherein thecontinuous phase is water or is aqueous-based, the gas phase cancomprise one or more gases selected from the group consisting of H₂S,CO₂, HCN, HCl, HBr, HF, HI, Cl₂, N₂O₄, NO₂, SO₂, SO₃ and NH₃. In otherembodiments, volatile organic acids can be employed as a gas phase inconjunction with a water or aqueous-based continuous phase. Suitablevolatile organic acids include formic acid and ethanoic acid.

Solubility of one or more gases in the continuous phase can becontrolled by several considerations including, but not limited to, thespecific identities of the gas and continuous phase, gas pressure, andtemperature of the continuous phase. For example, reaction rates of gasspecies with the continuous phase can be enhanced by highertemperatures, while gas solubility is generally increased by lowertemperatures.

In some embodiments, solute gradients, including ion concentrationgradients, affecting or inducing particle motion are formed viastripping one or more gas species from the continuous phase. In suchembodiments, the continuous phase is initially saturated with the gas tobe stripped. Once saturated, the gas can be stripped by exposing thesuspension to an atmosphere lacking the gas. Alternatively, or inaddition, a stripping gas can be bubbled or injected into the continuousphase for removal of the desired gas species.

In some embodiments, the solute gradient induces the suspended particlesto move toward the interface of the gas phase and continuous phase. Inother embodiments, the solute gradient induces the suspended particlesto move away from the interface. Movement of the particles in responseto solute gradients can concentrate the particles in a region of aconduit or container. Concentration of the particles can enable easyseparation or collection of the particles. Accordingly, methodsdescribed herein can be used for filtration applications.Advantageously, the methods do not require a filtration membrane,thereby significantly lowering power requirements and costs of routinemaintenance. In some embodiments, the particles are driven towardsbubbles in the suspension, wherein the particles attach to the bubblesfor subsequent removal or collection.

Particles suspended in the continuous phase and moved according tomethods described herein can have any desired composition. In someembodiments, the particles are inorganic compositions, such as metals,alloys, minerals, fine rock and/or semiconductor particles. Thesuspended particles may also be organic in nature including, but notlimited to, polymeric particles. In other embodiments, the suspendedparticles are biological including bacteria, viruses, nucleic acids,proteins, lipids or mixtures thereof. The suspended particles can alsohave complex architectures, such as core/shell constructs. The suspendedparticles, for example, can be micelles and related surfactantstructures. Moreover, the suspended particles are liquid particles, insome embodiments.

The suspended particles, solid or liquid, can exhibit surface chargesfor interacting with ionic concentration gradients formed by dissolutionand reaction of one or more gases with the continuous phase. Thesuspended particles can have any desired size. In some embodiments, thesuspended particles have an average size less than 1 μm. Average size ofthe suspended particles can be selected from Table I, in someembodiments.

TABLE I Average Size of Suspended Particles ≤500 nm 1-100 nm 10-200 nm50-150 nmAs set forth in Table I, the particles can be sufficiently small toprovide colloidal compositions. In other embodiments, average size ofthe suspended particles can be 1 μm or greater.II. Analytical Methods

In another aspect, analytical methods are described. In someembodiments, an analytical method comprises providing a suspension in achamber, the suspension comprising analyte particles suspended in acontinuous phase. The suspension is contacted with a gas phase toestablish at least one interface between the gas phase and continuousphase. One or more gases of the gas phase are transferred across theinterface to provide a solute gradient in the continuous phase, thesolute gradient concentrating the analyte particles in a region of thechamber. The concentrated analyte particles can subsequently be detectedand/or one or more properties of the analyte particles can bedetermined.

In some embodiments, for example, analyte particles are present in thesuspension at such low concentration that the particles cannot bereadily detected. Analyte particles, for example, can be present in thesuspension at nanomolar, picomolar or femtomolar levels prior to solutegradient formation. Notably, sufficient concentration of the analyteparticles induced by the solute gradient can render the particlesdetectable. In some embodiments, spectroscopic measurements and data canbe taken from the concentration of analyte particles. The spectroscopicdata may be sufficient to identify compositional parameters foraffirmative identification of the analyte. Moreover, analyte particlescan be sufficiently small to provide colloidal compositions foranalysis. Analyte particles may have an average size selected from TableI, in some embodiments.

Analyte particles can have any compositional parameters consistent withmethods described herein. Analyte particles, for example, can compriseinorganic compositions, polymeric compositions and/or biologicalcompositions. Analyte particles may be solid or liquid and can exhibitsurface charges. Moreover, solute gradients, including ion concentrationgradients, for inducing motion of the analyte particles can be producedin a manner consistent with that described in Section I herein.

III. Soluble Gas Detection

In another aspect, methods of detecting soluble gases are described. Amethod of detecting a soluble gas comprises providing a suspension in achamber and contacting the suspension with a gas sample to establish atleast one interface between the gas sample and continuous phase of thesuspension. Particle motion is detected in response to a solute gradientproduced by dissolution of one or more gases from the sample aftercrossing the interface. Formation and properties of the solute gradient,including ion concentration gradient(s), are described in detail inSection I herein.

Compositional parameters of the suspension can be selected according toproperties of the gas or gases to be detected. For example, for gasessoluble in polar or hydrophilic media, the continuous phase can be wateror aqueous-based solution as described in Section I herein. In someembodiments, the continuous phase can also be selected to react with thegas to provide an ion concentration gradient inducing particle motion.The suspended particles may exhibit surface charge to enhance particlemotion in response to a solute gradient, including an ion concentrationgradient. Careful control of suspension or colloid compositionalparameters can selectively detect the presence of one or more gases in agas sample, thereby enabling monitoring of various atmospheric orenvironmental species. In some embodiments, for example, harmful gasessuch as H₂S, SO₂ and/or SO₃ can be detected and monitored according tothe present methods. Degree of particle motion in response to thepresence of a gas species may be correlated to levels of the gas speciesin the atmosphere or local environment. Additionally, such monitoringcan be continuous or periodic.

IV. Surface Fouling Inhibition

In a further aspect, methods of inhibiting fouling of surfaces incontact with fluids are described. A method of inhibiting fouling of asurface in contact with a fluid comprises contacting the fluid with agas phase to establish at least one gas-fluid interface. One or moregases of the gas phase are transferred across the interface to provide asolute gradient in the fluid, the solute gradient inducing particlemotion in the fluid away from the surface. In some embodiments, forexample, the gas-fluid interface is adjacent to the surface, and thesolute gradient repels the particles from the surface. In otherembodiments, the gas-fluid interface is spaced apart from the surface,and the solute gradient attracts particles, thereby directing particlemotion away from the surface. Formation and properties of the solutegradient, including ion concentration gradient(s), are described indetail in Section I herein.

In some embodiments, the surface in contact with the fluid is porous.The porous surface, for example, can be a filter or a membrane. Filtersor membranes can have any desired construction and/or properties. Insome embodiments, the filter or membrane is part of a microfiltration orultrafiltration apparatus. The present method can extend filter ormembrane lifetime and/or extend operating periods between requiredmaintenance, such as filter or membrane cleaning or replacement.

As described herein, the gas phase can react with the fluid to providean ion concentration gradient. One or more gases can be selected suchthat ions forming the concentration gradient do not foul or interferewith the function of the surface contacting the fluid. In someembodiments, the fluid is a liquid. In other embodiments, the fluid is agas. The fluid can be in stationary contact with the surface.Alternatively, the fluid can be flowing across or though the surface,when porous. When stationary, the fluid can be periodically contactedwith the gas phase to establish or maintain the solute gradient. Whenflowing, the fluid can be continuously contacted with the gas phase toestablish or maintain the solute gradient.

Various embodiments of the invention have been described in fulfillmentof the various objectives of the invention. It should be recognized thatthese embodiments are merely illustrative of the principles of thepresent invention. Numerous modifications and adaptations thereof willbe readily apparent to those skilled in the art without departing fromthe spirit and scope of the invention.

The invention claimed is:
 1. A method of inducing or affecting particlemotion in a suspension comprising: contacting the suspension with a gasphase to establish at least one interface between the gas phase andsuspension continuous phase; transferring one or more gases of the gasphase across the interface to provide a solute gradient in thecontinuous phase, the solute gradient inducing or affecting motion ofthe suspended particles.
 2. The method of claim 1, wherein the solutegradient induces the suspended particles to move toward the interface.3. The method of claim 1, wherein the solute gradient induces thesuspended particles to move away from the interface.
 4. The method ofclaim 1, wherein the one or more gases are dissolved in the continuousphase.
 5. The method of claim 4, wherein the one or more gases reactwith the continuous phase to provide an ion concentration gradient. 6.The method of claim 1, wherein the one or more gases interact with anadditive in the continuous phase to provide the solute gradient.
 7. Themethod of claim 1, wherein the one or more gases are transferred acrossthe interface out of the continuous phase.
 8. The method of claim 1,wherein the suspended particles are dispersed throughout the continuousphase prior to contact of the suspension with the gas phase.
 9. Themethod of claim 1, wherein the suspension is a colloid.
 10. The methodof claim 1, wherein the continuous phase is water or aqueous-based. 11.The method of claim 1, wherein the continuous phase is a gas.
 12. Themethod of claim 1, wherein the suspended particles exhibit surfacecharge.
 13. The method of claim 1, wherein the suspended particles areconcentrated by the solute gradient.
 14. The method of claim 13 furthercomprising isolating the suspended particles from the suspension. 15.The method of claim 1, wherein a plurality of gases are transferredacross the interface.
 16. The method of claim 1, wherein the suspendedparticles comprise biological species selected from the group consistingof bacteria, viruses, nucleic acids, proteins, lipids and mixturesthereof.
 17. An analytical method comprising: disposing a suspension ina chamber, the suspension comprising analyte particles suspended in acontinuous phase; contacting the suspension with a gas phase toestablish at least one interface between the gas phase and continuousphase; transferring one or more gases of the gas phase across theinterface to provide a solute gradient in the continuous phase, thesolute gradient concentrating the analyte particles in a region of thechamber; and detecting the concentrated analyte particles and/ordetermining one or more properties of the concentrated analyteparticles.
 18. A method of inhibiting fouling of a surface in contactwith a fluid comprising: contacting the fluid with a gas phase toestablish at least one gas-fluid interface; transferring one or moregases of the gas phase across the interface to provide a solute gradientin the fluid, the solute gradient inducing particle motion in the fluidaway from the surface.
 19. The method of claim 18, wherein the gas-fluidinterface is adjacent to the surface, and the solute gradient repelsparticles from the surface.
 20. The method of claim 18, wherein thegas-fluid interface is spaced apart from the surface, and the solutegradient attracts particles, thereby directing particle motion away fromthe surface.
 21. The method of claim 18, wherein the surface is porous.22. The method of claim 21, wherein the surface is a filter or membrane.23. A method of detecting a soluble gas comprising: providing asuspension in a chamber, the suspension comprising particles suspendedin a continuous phase; contacting the suspension with a gas sample toestablish at least one interface between the gas sample and thecontinuous phase; and detecting particle motion in the continuous phasein response to a solute gradient produced by dissolution of one or moregases from the sample after crossing the interface.